Poor focus in Cycles render
Firstly I'd like to thank you both very much for spending the time reading my question.

I continued to blunder around trying to solve my problem when I had a light bulb moment and noticed that in the 'sampling' section of the render panel it was set at  Render :10 and Preview:10,  obviously the default setting! And being new to blender I hadn't noticed. Anyway, I whacked up the Render value to 100, then 500 &amp; finally 1000 and low &amp; behold I got the razor sharp image I wanted, and spent the rest of the day feeling very pleased with myself.

So this is a case of self help, but thank you so much for reading my question!